With the increase in global warming, technologies for acquiring new energy without using fossil fuels have been developed, and the development of technologies for energy recovery from various biomass and renewable organic sources have been advanced in many areas. For example, hydrogen has attracted attention as a fuel that causes no environmental pollution and is currently mainly manufactured from fossil fuels. In order to acquire clean energy, the hydrogen fermentation by microorganisms using renewable organic resource as raw materials has been desired.
The renewable organic resources as raw materials used in the hydrogen fermentation include food waste, agricultural waste, and the like. Food waste includes food scraps in complex buildings (restaurants, hotels, offices, shops and the like), wastes of confectionery and bread in food factories, fruit processing remains, and the like. Using the above-mentioned renewable organic resources as raw materials, the hydrogen fermentation is performed using hydrogen-producing bacteria. As the hydrogen-producing bacteria, sludge in a solubilization tank at the pretreatment of methane fermentation is used as seed sludge. Obligate anaerobic bacteria and facultative anaerobic bacteria, which are hydrogen-producing bacteria, reside in this type of sludge. The Obligate anaerobic bacteria include Clostridum butyricum and Clostridum beijerinckii, and the facultative anaerobic bacteria include Enterobacter aerogenes and the like. The above-mentioned hydrogen-producing bacteria produce hydrogen via hydrogen fermentation of an organic matter as a substrate by a reaction with a retention time of 1 to 2 days.
As described above, an attempt to recover hydrogen from organic resources by hydrogen fermentation has been already reported. For example, Patent Documents 1 and 2 describe a method for recycling obtained hydrogen as an electrical energy. In addition, Patent Document 3 describes that the fermentation is performed under reduced pressure in order to lower the hydrogen partial pressure. Furthermore, Patent Document 4 describes a method and an apparatus for performing hydrogen fermentation using renewable organic waste as a raw material.    Patent Document 1: Japanese Patent Application Laid-Open No. 2001-23677    Patent Document 2: Japanese Patent Application Laid-Open No. 2001-229955    Patent Document 3: Japanese Patent Application Laid-Open No. 07-31998    Patent Document 4: Japanese Patent Application Laid-Open No. 2003-135088